Presumably the volatility inherent to “volatile chemicals” makes it challenging to reproduce on-demand. I’d imagine you’d need something like dozens of base compounds, alcohols and acids to create esters and carrier media, some way of protecting all of it from oxygen, a hyper-accurate mixing device that can then by hyper-cleaned between each scent, since our noses would be too sensitive to allow even a small amount of cross-contamination…and then, why stop at smell? You basically already have everything you need for taste as well. Insert some lab-grown tissues and/or fibers, and we’ve invented the Star Trek replicator!